package com.dmall.queue;

/**
 * 循环队列
 * 此循环队列未记录循环队列的个数，即：size变量的值
 * @param <E> 泛型
 * @author xiao1.wang
 * @date 2019-06-28 20:33:41
 */
public class CircleQueue<E> implements Queue<E> {

    private E[] data;
    private int front, tail;

    public CircleQueue(int capacity) {
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
    }

    public CircleQueue() {
        this(10);
    }

    @Override
    public void enqueue(E e) {
        if ((tail + 1) % data.length == front) {
            resize(2 * getCapacity());
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
    }

    @Override
    public E dequeue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("Can't dequeue from an empty queue.");
        }
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        if (getSize() <= getCapacity() / 4 && getCapacity() / 2 > 0) {
            resize(getCapacity() / 2);
        }
        return ret;
    }

    @Override
    public E getFront() {
        if (isEmpty()) {
            throw new IllegalArgumentException("Can't getFront from an empty queue.");
        }
        return data[front];
    }

    @Override
    public int getSize() {
        return (tail - front + data.length) % data.length;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    public int getCapacity() {
        return data.length - 1;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("Queue: size = %d , capacity = %d\n", getSize(), getCapacity()));
        res.append("front [");
        for(int i = front ; i != tail ; i = (i + 1) % data.length){
            res.append(data[i]);
            if((i + 1) % data.length != tail) {
                res.append(", ");
            }
        }
        res.append("] tail");
        return res.toString();
    }

    private void resize(int newCapacity) {
        E[] newData = (E[]) new Object[newCapacity + 1];
        int size = getSize();
        for (int i = 0; i < size; i++) {
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    public static void main(String[] args){
        CircleQueue<Integer> queue = new CircleQueue<>();
        for(int i = 0 ; i < 10 ; i ++){
            queue.enqueue(i);
            System.out.println("enqueue: "+queue);

            if(i % 3 == 2){
                queue.dequeue();
                System.out.println("dequeue: "+queue);
            }
        }
    }
}
